1. Field of the Invention
This invention relates to a pressure sensor for sensing fluid pressure to detect gas leakage or the like.
2. Discussion of the Related Art
For example, a pressure sensor for detecting gas leakages which is intended to be operated at a slight pressure of a water column of 20 to 80 mm is, as shown in FIG. 16, usually provided with a diaphragm 2 in a pressure receiving chamber 1 thereof. This diaphragm 2 is provided to cause a plunger 3 to move in association with the inverse movement of the diaphragm 2 in accordance with any change in the gas pressure. As a result of this, a switch 4 is turned on or off in synchronization with the movement of the plunger 3.
In this case, a pressure receiving case 5 which encloses the pressure receiving chamber 1 is secured to a predetermined device by screws 6 or the like and connects the pressure receiving chamber 1 to a gas passage through pressure receiving port 7.
However, this pressure sensor is put together in a way like that shown in FIG. 16, in which a case 8 accommodating the switch 4 and the pressure receiving case 5 are welded together. In this structure, where the diaphragm 2 and the switch 4 have already been integrated in the pressure sensor, the following problem is raised: that is, diaphragm inverse movement tests cannot be carried out separately from testing on-off switch operation. As a result of these, if either one of these tests shows the corresponding parts to be defective, the whole pressure sensor, including remaining part that may well be satisfactory, is judged to be a defective product, and this causes manufacturing yields to be poor.